Robust Fiducial Marker for Flexible Surfaces

ABSTRACT

The present invention discloses fiducial marker systems or tag systems and methods to detect and decode a tag. In one aspect, a tag comprises four corners. Two upper corners are interconnected to form a detection area. Two lower corners are interconnected to form another detection area. The detection areas are interconnected by a path. The path divides the space between the detection areas into two coding areas. In another aspect, a tag comprises four corners. The four corners are interconnected by multiple paths. The multiple paths divide the space defined by the four corners into multiple coding areas.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. provisional patent applicationSer. No. 62/729,427, filed Sep. 11, 2018, the entire content of which isincorporated herein by reference.

FIELD OF INVENTION

This invention generally relates to visual fiducial marker technology.

BACKGROUND OF THE INVENTION

A fiducial marker (also known as tag) is an object placed in the fieldof view of an imaging system which appears in the image produced, foruse as a point of reference or a measure. Such tags are artificiallandmarks designed to be easy to recognize and distinguish from oneanother. A fiducial marker system generally includes tags, cameras forcapturing images containing these tags, and detection software fordetecting and/or identifying these tags.

Fiducial marker systems have been widely used in applications such asaugmented reality, Simultaneous Localization and Mapping (SLAM), humanrobot interaction, package and human detection and tracking, and factoryand warehouse management. In these applications, tags are generallydesigned as two-dimensional (“2D”) barcodes. When in use, they areattached to or printed on the surface of an object. Detection softwarecomputes the precise three-dimensional (“3D”) position, orientation, andidentity of the tags relative to the camera.

Prior art fiducial marker systems, such as AprilTag and its predecessorsARToolkit and ARTag, use tags having a square-shaped black border. Tagdetection is accomplished by detecting square-shaped black border(s) inan image. Once a tag is detected, its payload within the black border isdecoded against a database of known tags. However, such design has manydrawbacks. First, tags are often attached to or printed on surfaces thatmay often be warped, bended, or wrinkled. As such, their square-shapedblack borders can be easily distorted and lose the square shape,therefore leading to the failure of their detection. This drawbacksignificantly limits the prior art fiducial systems' applications inrough or difficult environments (e.g., applications where tags worn by ahuman).

Second, if any portion of the prior art tag's border is blocked orcovered (e.g., by a human finger) and the square-shaped black borderbecomes an open loop, the detection software will fail to detect thetag. Thus, the prior art systems' overall robustness suffers.

The other drawback of the prior art fiducial marker systems is that thesquare-shaped black border takes up significant amount of tag space,limiting the tags' coding space. As such, it is difficult to reduce thesize of the tags if certain amount of coding space is needed.

Thus, a new fiducial marker system is needed to solve the aboveproblems.

SUMMARY OF THE INVENTION

The present invention discloses tags, tag systems, and methods to detectand decode tags. A tag has a square or rectangular shape and is dividedinto a plurality of cells based on a grid pattern (i.e., arranged inrows and columns). The cells are in uniform shape and size and may be insquare or rectangular shape. Each cell is either dark color or lightcolor. Ideally, black color is used as dark color and white color isused as light color to maximize the success rate of tag detection underreal-life lighting conditions of tags, which may not produce idealimages of the tags. A cell located along an edge of the tag is called a“border cell”; and a cell not located along any edge of the tag iscalled an “interior cell.”

In one embodiment, each cell in a first full row of cells along a firstedge of the tag (e.g., the top edge) being dark color. The first fullrow of cells includes a first corner cell and a second corner cell ofthe tag. The first full row of cells defines a first area of the tag.Each cell in a second full row of cells along a second edge of the tag(e.g., the bottom edge) being dark color, and the first edge is oppositeto the second edge. The second full row of cells includes a third cornercell and a fourth corner cell of the tag. The second full row of cellsdefines a second area of the tag. The first area and the second area areinterconnected by a path of connected cells in dark color, wherein eachcell in the path of connected cells is an interior cell. Two cells areconnected if they share a common cell border and are both in dark color.The remaining cells of the plurality of cells (i.e., cells not in thefirst and second rows and the path) are either dark color or lightcolor. To detect the tag in an image, the present invention detects thefour corner cells first in the image. If the four corner cells aredetected, the present invention determines whether the first and secondcorner cells are interconnected in the first area in the image andwhether the third and fourth corner cells are interconnected in thesecond area in the image. If so, the present invention determineswhether the first area and the second area are interconnected by a pathof connected dark interior cells in the image. If the first area and thesecond area are interconnected by a path of connected dark interiorcells in the image, the tag is detected in the image and the presentinvention tries to decode the tag in the image.

In one embodiment, the path of connected dark interior cells form astraight line.

In another embodiment, the four corner cells are interconnected bymultiple paths of connected dark cells. To detect the tag in an image,the present invention first detects the four corner cells in the image.Next, the present invention determines whether the four corner cells areinterconnected by paths containing connected dark cells in the image. Ifso, the tag is detected in the image and the present invention thentries to decode the tag in the image.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter, which is regarded as the invention, is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features and also theadvantages of the invention will be apparent from the following detaileddescription taken in conjunction with the accompanying drawings.Additionally, the leftmost digit of a reference number identifies thedrawing in which the reference number first appears.

FIG. 1A illustrates a prior art tag design.

FIG. 1B illustrates an example of a prior art tag.

FIG. 1C illustrates a problem with the prior art tag design illustratedin FIG. 1A.

FIG. 1D illustrates another problem with the prior art tag designillustrated in FIG. 1A.

FIG. 2A illustrates a tag design, according to one embodiment of thepresent invention.

FIG. 2B illustrates an example of a tag, according to one embodiment ofthe present invention.

FIG. 3 illustrates a process of detecting a tag, according to oneembodiment of the present invention.

FIG. 4A illustrates how the tag design in FIG. 2A can void the problemillustrated in FIG. 1C.

FIG. 4B illustrates how the tag design in FIG. 2A can mitigate theproblem illustrated in FIG. 1D.

FIG. 5A illustrates a tag design, according to one embodiment of thepresent invention.

FIG. 5B illustrates an example of a tag, according to one embodiment ofthe present invention.

FIG. 6A illustrates a tag design, according to one embodiment of thepresent invention.

FIG. 6B illustrates an example of a tag, according to one embodiment ofthe present invention.

FIG. 7 illustrates a tag design, according to one embodiment of thepresent invention.

FIG. 8A illustrates a tag design, according to one embodiment of thepresent invention.

FIG. 8B illustrates an example of a tag, according to one embodiment ofthe present invention.

DETAILED DESCRIPTION

Detailed description of the present invention is provided below alongwith figures and embodiments, which further clarifies the objectives,technical solutions, and advantages of the present invention. It isnoted that schematic embodiments discussed herein are merely forillustrating the invention. The present invention is not limited to theembodiments disclosed.

FIG. 1A illustrates a prior art tag design. As shown, the prior art tagdesign embodies a square-shaped 8×8 grid, having a total of 64 squareunits (a.k.a., cells). Each square unit is either in black color orwhite color. The border section 101 (the hatched section shown in FIG.1A) is always in black color for tag detection. If the detectionsoftware cannot detect the square-shaped black border in an imagecontaining the tag, the tag is not detected. Detection is generallyaccomplished by computer vision algorithms, such as Union-find forboundary detection and principal component analysis (PCA) for cornerdetection. The dotted section 102 is used for coding, e.g., by assigningblack or white color to each square unit. Thus, although the tag has atotal of 64 square units, only 36 square units are actually used forcoding, whose maximum coding space is 2³⁶. The coding area to total tagarea ratio is 9:16, which is just slightly above 50%. FIG. 1Billustrates an example of a tag according to this prior art design.

However, the prior art tag design illustrated in FIG. 1A has manydrawbacks. FIG. 1C illustrates such a problem where the tag shown inFIG. 1B is warped such that the square-shaped black border captured inan image is not square-shaped anymore. Nor could the detection softwarereconstruct the square-shaped border by simply adjusting the view pointbecause the tag itself has warped. This could happen when the tag isprinted on or attached to a soft or uneven surface which may be warped,stretched, distorted, or wrinkled frequently. For example, in a factoryand warehouse management application, some tags are printed or attachedon workers' uniforms or clothes. When a worker moves around, the tag onhis/her uniform can get easily warped, stretched, or distorted. As aresult, the detection software won't be able to detect the tag. If thiskind of failure happens too often and widespread, the whole system maystop working properly.

FIG. 1D illustrates another problem with the prior art tag designillustrated in FIG. 1A. As shown, the tag's square-shaped black borderis partially covered by a person's thumb. The thumb breaks the closedloop of the border, and if any portion of the square-shaped black borderis blocked or covered, the detection software will not be able to detectthe tag. Because the border section 101 (shown in FIG. 1A) takes up 7/16of the total tag area, the probability that the border section of thetag is blocked or covered compared to the probability that the codingsection 102 (shown in FIG. 1A) is covered or blocked by an object is 7to 9. In reality, the ratio should be even higher because when thecoding section 102 is blocked or covered by an object (e.g., a hand),the border section is also likely blocked or covered by the same objector any extension of the object (e.g., forearm). As such, the prior arttag design illustrated in FIG. 1A is prone to detection failure.

FIG. 2A illustrates a new tag design, according to one embodiment of thepresent invention. As shown, the new tag design embodies arectangular-shaped 8×7 grid, including 56 square units or cells. Section201 (the hatched area) is a full row of square units (including twocorner square units) along the top edge of the tag. It contains 7 squareunits. Section 202 (the crosshatched area) is a full row of square units(including the other two corner square units) along the bottom edge ofthe tag. Section 202 contains 7 square units. The top edge is oppositeto the bottom edge. The middle column, namely section 203 (the dottedarea) contains 6 square units. Section 201, section 202 and section 203(collectively, “the detection area”) are always in black color. Thedetection area is used for tag detection. Specifically, the detectionmethod is to check whether the detection area is interconnected, meaningthat it is in continuous black color. This design is more effective androbust in dealing with rough or difficult to control environments. Theremaining section contains 36 square units and is used for coding. Andeach of the remaining 36 square units is either black color or whitecolor. It should be noted that although descriptions of the embodimentsin the present application use black and white colors for the squareunits (or cells), other dark and light colors may also be used as longas they have adequate contrast and can be distinguished in an image byprocessing software.

The 8×7 grid is used for explaining the embodiment only. Other gridpatterns may be used as well. For instance, the shape of a tag may besquare or rectangular, and the tags may have various numbers of rows,columns, and square units.

FIG. 2B illustrates an example of a tag according to the designillustrated in FIG. 2A. The top and bottom rows are in black color andthere is a middle column which is also in black color. Thus, the two topcorner cells are interconnected by black cells in the top row. The twobottom corner cells are interconnected by black cells in the bottom row.The top and bottom rows are interconnected by black cells of the middlecolumn. Patterns formed by black and white cells are configured incoding areas. In applications, a tag may be placed with differentorientation settings and may also be rotated sometimes. For instance, ifthe tag shown in FIG. 2B is rotated by ninety degrees anticlockwise, thetop and bottom rows become the left and right columns and the middlecolumn becomes a middle row. The orientation change doesn't affectdetection of a tag, since the viewpoint may be adjusted by processingsoftware.

FIG. 3 illustrates a process 300 of detecting a tag, such as onefollowing the design illustrated in FIG. 2A. A system for using a tagmay include the tag, a working camera, and a processing unit (e.g., acomputer) having software or program containing instructions fordetecting and decoding the tag. At the beginning, the tag is attached toa target object. At step 301, the process 300 receives an image of thetag captured by the working camera. As shown in FIGS. 1C and 1D, the tagcould be warped or occluded.

At step 302, the process 300 scans the image to find the four corners ofthe tag, which should be in black color. Various computer visionalgorithms may be used for finding the four corners. For example, theprocess 300 may use Harris corner detector to detect the four corners ofthe tag (e.g., the outermost four corners of all corners detected fromthe tag image). If the four corners are detected, then the process goesto step 303. Otherwise, tag detection fails and the process reportsfailure.

At step 303, the process 300 scans the image to determine whether thedetection area (as defined in FIG. 2A) is interconnected in black color.Specifically, the process 300 determines whether two of the four tagcorners are interconnected along the path of the square units of section201 of the tag (as shown in FIG. 2A). Here, interconnection does notrequire that all 7 square units of section 201 be identified, in perfectalignment, or square-shaped in the image. Rather, interconnection isachieved when the square units of section 201 of the tag identified fromthe image (whether all 7 of them or part of them) together with the twotag corners are interconnected in black color. Similarly, the process300 determines whether the other two tag corners are interconnectedalong the path of the square units of section 202 of the detection area(also shown in FIG. 2A) and whether the two sections 201 and 202 areinterconnected along the path of the square units of section 203 (alsoshown in FIG. 2A). If the detection area is not interconnected, then theprocess reports failure. Otherwise, the tag is detected, and the processgoes to step 304, where the tag is decoded.

The new tag design illustrated in FIG. 2A and its detection processillustrated in FIG. 3 have many advantages over the prior art tag designand detection method. For example, FIG. 4A illustrates how the design inFIG. 2A can void the problem illustrated in FIG. 1C. As shown, the tagin FIG. 4A is warped, similar to the example shown in FIG. 1C. However,according to the process illustrated in FIG. 3, the tag's detection areais still interconnected. As such, the tag in FIG. 4A can still bedetected, whereas the tag in FIG. 1C could not be detected by the priorart method.

As another example, FIG. 4B illustrates how the design in FIG. 2A canmitigate the problem illustrated in FIG. 1D. Similar to the example inFIG. 1D, the right edge of the tag in FIG. 4B is covered by a person'sthumb. However, this won't affect the detection of the tag in FIG. 4Bbecause the detection area of the tag is still interconnected.

In addition, even though part of the coding area in FIG. 4B is covered,the detection software may still be able to do a partial decoding andnarrow down the results to a small range or number of codes. Based onother available information, such as the tag's current location andother tags' historical location data, the system may further narrow downthe range or number of codes.

Another advantage of the tag design illustrated in FIG. 2A is that itscoding area to total tag area ratio is 9:14, which is better than thatof the prior art design. When the coding area is the same, the overallsize of the new design is smaller than that of the prior art design.

FIG. 5A illustrates another tag design, according to one embodiment ofthe present invention. As shown, the design is similar to the designillustrated in FIG. 2A. The difference is that instead of using themiddle column of square units (section 203 in FIG. 2A) as a designatedarea for detection purposes, the middle column of square units is nowused for coding as well. This further improves the coding area to totaltag area ratio to 3:4 or 75%. Meanwhile, sections 501 and 502 are stilldesignated for detection purposes. However, the coding area should haveat least one path of connected square units interconnecting section 501and section 502. Here, two square units are connected if the two squareunits are all in black color and share a common border. The detectionmethod here is to check whether there is at least one path of connectedsquare units interconnecting section 501 and section 502. Compared tothe design illustrated in FIG. 2A, the design in FIG. 5A is moreflexible and robust. In addition, it has more coding space than thedesign in FIG. 2A does. FIG. 5B illustrates an example of a tag,according to one embodiment of the present invention.

In one embodiment, a modified version of the process 300 may be used fordetecting a tag according to the design illustrated in FIG. 5A. Themodified version of the process 300 still scans a tag image to identifythe four corners. Then, the modified process determines whether twocorners are interconnected along the path of the square units of section501 and whether the other two corners are interconnected along the pathof the square units of section 502. Like the process 300, the modifiedprocess determines whether there is at least one path of connectedsquare units (or connected black cells) that interconnects section 501and section 502. If any of the above steps fails, the detection processreports detection failure and abort the detection process.

In another embodiment of the present invention, as shown in FIG. 6A, athin white color border 601 is added around the tag. Preferably, thewidth of the white color border 601 is about ⅓ of the width of thesquare. This white color border creates a sharp contrast with thedesignated detection area 602 of the tag and makes it easier fordetection. FIG. 6B illustrates an example of a fiducial marker,according to one embodiment of the present invention. As shown, thebackground 603 may have a color too close to the color of the designateddetection area 602. Adding a thin white color border 601 would create asharp contrast between the designated detection area 602 and the thinwhite color border 601 so that it is easier to detect the designateddetection area 602.

FIG. 7 illustrates another embodiment of the present invention based onthe embodiment shown in FIG. 2A. As shown, a five-digit code (each digitmay be a number or a letter) is added to the bottom of the tag and partof the digits overlap with the square units in section 202. Thus, aportion of an image of the code is presented using the bottom row of thetag. Alternatively, a portion of the image may also be presented usingthe top row of the tag. In addition, the top and bottom rows may be usedto present two codes for a tag. The five-digit code provides anadditional means for error correction on the tag's code. It alsoprovides a convenient way of identification by human eyes. For example,if the tag's code cannot be completely identified due to, for example,part of the coding area is covered (as illustrated in FIG. 4B), thefive-digit code, if can be detected and identified by the detectionsoftware, can help to further identifies the tag's code. In oneembodiment, the dimension of a digit number/letter is roughly 1×1⅓ of asquare unit so the recognition range for the digit number/letter iscomparable to ½ of the marker in the best case. The five-digit code maybe recognized by deep leaning algorithms, which provide robust errorcorrections when the recognition confidence level of traditionalcomputer vision based marker recognition is low. Of course, the codecould be four or other number of digits as well depending on theapplication. For instance, the code may contain one or more elements.The elements may include a numerical number, a letter, a character, or asymbol.

FIG. 8A illustrates another tag design, according to yet anotherembodiment of the present invention. According to this tag design, thefour corner square units 801, 802, 803, and 804 are always in blackcolor. In addition, this design requires that the four corner squareunits 801-804 be interconnected by other black square units in the tag.For example, FIG. 8B illustrates a valid tag under the designillustrated by FIG. 8A. This design further increases the coding spaceof the tag. In addition, this tag design improves the robustness fordetection because it does not depend on whether a specific detectionarea can be identified from an image. As such, it can deal with warpedor uneven surface better than the above disclosed embodiments.

Similar to the embodiment shown in FIG. 6A, a thin border region inwhite or light color may be placed around the tag shown in FIGS. 8A and8B. The thin border region creates a sharp contrast with the corners ofthe tag and makes it easier for detection.

FIG. 9 illustrates a process 900 of detecting a tag, such as onefollowing the design illustrated in FIG. 8A. At step 901, the process900 receives an image of a tag captured by a working camera. As shown inFIGS. 1C and 1D, the tag could be warped or occluded.

At step 902, the process 900 scans the image to find the four corners ofthe tag, which should be in black color. Various computer visionalgorithms may be used for finding the four corners. For example, theprocess 900 may use Harris corner detector to detect the four corners ofthe tag. If the four corners are detected, then the process goes to step903. Otherwise, tag detection fails and the process reports failure.

At step 903, the process 300 scans the image to determine whether thefour corners are interconnected in black color. One way to determinewhether the four corners are interconnected is to determine whetherthere is at least one path of connected square units from one tag cornerto the other three tag corners. If the detection area is notinterconnected, then the process reports failure. Otherwise, the tag isdetected, and the process goes to step 904, where the tag is decoded.

In embodiments discussed above, grid dimensions, and orientations (e.g.,8×7 grid) of the invention have been disclosed. Those having ordinaryskill in the art will understand that changes can be made to thespecific embodiments, grid dimensions, and orientations withoutdeparting from the spirit and scope of the invention.

Thus, although specific embodiments of the invention have beendisclosed, those having ordinary skill in the art will understand thatchanges can be made to the specific embodiments without departing fromthe spirit and scope of the invention. The scope of the invention is notto be restricted, therefore, to the specific embodiments. Furthermore,it is intended that the appended claims cover any and all suchapplications, modifications, and embodiments within the scope of thepresent invention.

1. A method for detecting and decoding a square-shaped orrectangular-shaped tag captured in an image, the tag being divided intoa plurality of cells based on a grid pattern, each cell in a first fullrow of cells along a first edge of the tag being dark color, the firstfull row of cells including a first corner cell and a second corner cellof the tag, the first full row of cells defining a first area of thetag, each cell in a second full row of cells along a second edge of thetag being dark color, the first edge being opposite to the second edge,the second full row of cells including a third corner cell and a fourthcorner cell of the tag, the second full row of cells defining a secondarea of the tag, the first area and the second area being interconnectedby a path of connected cells in dark color, each cell in the path ofconnected cells located not along any edge of the tag, remaining cellsof the plurality of cells being either dark color or light color, themethod comprising: detecting the first, second, third, and fourth cornercells in the image; determining whether the first and second cornercells are interconnected in the first area in the image; determiningwhether the third and fourth corner cells are interconnected in thesecond area in the image; determining whether the first area and thesecond area are interconnected by the path of connected cells in theimage; and decoding the tag based on colors of the remaining cells ofthe plurality of cells.
 2. The method of claim 1, wherein the path ofconnected cells forms a straight line.
 3. The method of claim 1, whereinsaid decoding is also based on colors of the cells in the path ofconnected cells.
 4. The method of claim 1, wherein the tag is surroundedby a border region in light color.
 5. The method of claim 1, wherein aportion of an image of a code is presented using the first or secondarea, the code including at least one of a plurality of elements, theplurality of elements including a numerical number and a letter.
 6. Amethod comprising: attaching a tag to a target object, wherein the tagis a square-shaped or rectangular-shaped tag, the tag being divided intoa plurality of cells based on a grid pattern, each cell in a first fullrow of border cells being dark color, the first full row of border cellsincluding a first corner cell and a second corner cell of the tag, thefirst full row of border cells defining a first area of the tag, eachcell in a second full row of border cells being dark color, the secondfull row of border cells including a third corner cell and a fourthcorner cell of the tag, the second full row of border cells defining asecond area of the tag, the first area and the second area beinginterconnected by a path of connected interior cells in dark color,remaining cells of the plurality of cells being either dark color orlight color; using a camera to capture an image comprising the tag;detecting the first, second, third, and fourth corner cells in theimage; determining whether the first and second corner cells areinterconnected in the first area in the image; determining whether thethird and fourth corner cells are interconnected in the second area inthe image; determining whether the first area and the second area areinterconnected by the path of connected interior cells in the image; anddecoding the tag based on colors of the remaining cells of the pluralityof cells.
 7. The method of claim 6, wherein the path of connectedinterior cells forms a straight line.
 8. The method of claim 6, whereinsaid decoding is also based on colors of the cells in the path ofconnected interior cells.
 9. The method of claim 6, wherein the tag issurrounded by a border region in light color.
 10. The method of claim 6,wherein a portion of a code's image is presented using the first orsecond area, the code including at least one of a plurality of elements,the plurality of elements including a numerical number and a letter. 11.A system for using a fiducial marker, comprising: a square-shaped orrectangular-shaped tag, the tag being divided into a plurality of cellsbased on a grid pattern, each cell in a first full row of cells along afirst edge of the tag being dark color, the first full row of cellsincluding a first corner cell and a second corner cell of the tag, thefirst full row of cells defining a first area of the tag, each cell in asecond full row of cells along a second edge of the tag being darkcolor, the first edge being opposite to the second edge, the second fullrow of cells including a third corner cell and a fourth corner cell ofthe tag, the second full row of cells defining a second area of the tag,the first area and the second area being interconnected by a path ofconnected cells in dark color, each cell in the path of connected cellslocated not on any edge of the tag, remaining cells of the plurality ofcells being either dark color or light color; a camera for capturing animage comprising the tag; and a processing unit that executesinstructions to perform the steps comprising: detecting the first,second, third, and fourth corner cells in the image, determining whetherthe first and second corner cells are interconnected in the first areain the image, determining whether the third and fourth corner cells areinterconnected in the second area in the image, determining whether thefirst area and the second area are interconnected by the path ofconnected cells in the image, and decoding the tag based on colors ofthe remaining cells of the plurality of cells.
 12. The system of claim11, wherein the path of connected cells forms a straight line.
 13. Thesystem of claim 11, wherein the path of connected cells contains codedinformation.
 14. The system of claim 11, wherein the tag is surroundedby a border region in light color.
 15. The system of claim 11, wherein aportion of a code's image is presented using the first or second area,the code including at least one of a plurality of elements, theplurality of elements including a numerical number and a letter.
 16. Atag as a fiducial marker, comprising: a plurality of cells arranged in agrid pattern, the plurality of cells forming a square or rectangularshape, each cell in a first full row of cells along a first edge of thetag being dark color, the first full row of cells including a firstcorner cell and a second corner cell of the tag, the first full row ofcells defining a first area of the tag, each cell in a second full rowof cells along a second edge of the tag being dark color, the first edgebeing opposite to the second edge, the second full row of cellsincluding a third corner cell and a fourth corner cell of the tag, thesecond full row of cells defining a second area of the tag, the firstarea and the second area being interconnected by a path of connectedinterior cells in dark color, remaining cells of the plurality of cellsbeing either dark color or light color.
 17. The tag of claim 16, whereinthe path of connected cells forms a straight line.
 18. The tag of claim16, wherein the path of connected cells contains coded information. 19.The tag of claim 16, wherein a portion of an image of a code ispresented using the first or second area, the code including at leastone of a plurality of elements, the plurality of elements including anumerical number and a letter.
 20. A method for detecting and decoding asquare-shaped or rectangular-shaped tag captured in an image, the tagbeing divided into a plurality of cells based on a grid pattern andhaving a first, second, third, and fourth corner cells being in darkcolor and interconnected by a plurality of connected cells in darkcolor, each cell, except the first, second, third, and fourth cornercells and the plurality of connected cells, being either dark color orlight color, the method comprising: detecting the first, second, third,and fourth corner cells in the image; determining whether the first,second, third, and fourth corner cells are interconnected by theplurality of connected cells in dark color in the image; and decodingthe tag based on colors of the cells except the first, second, third,and fourth corner cells.